The simulation of a deep convective cloud in complex orography: the 15 July 2007 case from COPSRalph Burton, Alan Gadian, Alan Blyth, Stephen Mobbs National Centre for Atmospheric Science, University of Leeds, UK contact:

ralph@env.leeds.ac.uk

Run name

BL scheme Land surface

Comments

THERM_YSU

YSU Thermal diffusion

Very shallow, very isolated cloud.

THERM_MYJ

MYJ Thermal diffusion

Very shallow cloud.

NOAH_YSU

YSU NOAH LSM

Very shallow cloud.

NOAH_MYJ

MYJ NOAH LSM

Deep cloud extending to approx 12km in altitude.

Numerical and dynamical parameters

Nest number1 2

Grid sizes and resolution

550x550 x 50 vertical levels, 3.6km

301x241 x 50 vertical levels, 1.2km

Time step 18s 6sCumulus parametrisation

None None

Microphysics Morrison MorrisonRadiation (SW) Dudhia DudhiaRadiation (LW) RRTM RRTM

Difference plots along AB, showing q(NOAH_MYJ) - q(THERM_MYJ) for (a) 08Z and (b) 11Z. (coloured contours, g/kg)

Difference plots of q2(NOAH_MYJ)-q2(THERM_MYJ) for (a) 13Z, (b) 14Z and (c) 15Z. Also shown are isosurfaces of cloud-water mixing ratio at a value of 0.1g/kg. The range of displayed values ranges from -0.001kg/kg (coloured deep blue) to 0.001kg/kg (coloured red).

Vertical velocities and wind vectors along the cross-section defined in the leftmost plot. for the NOAH-MYJ run at 15Z. Also shown are the 95% and 100% RH contours (solid lines). Wind vectors are constructed such that if the head of one vector touches the tail of another, the horizontal windspeed is 5m/s.

COPSConvective and orographically-induced

precipitation study

Location of the COPS field phase. Map taken from the COPS brochure [1]. For an overview of the COPS campaign see [2].

Isolated, deep cloud formed on the 15th July from 13-16Z. This was perhaps the only instance of such a cloud during the whole COPS experiment. The ability of a numerical model (WRF) to simulate this cloud is the subject of this study.Photo from the Science Director Summary,www.cops2007.de

WRF modelling: sensitivity to boundary-layer and land-surface schemes

Domains used in the WRF simulation. The outer domain is at 6.1km resolution; the inner domain at 2.1km resolution.

This study presents a sensitivity test consisting of four runs. Features common to all runs are contained in Table I; differences between runs are described in Table II.

Table I Table II

Results I: sensitivity to BL scheme

To the left is shownvertical velocities at 1.5kmfor the THERM_YSU run at 14Z.A clear surface convergencesignal is seen: this is common toall runs.

Results II: sensitivity to land surface scheme

Difference plots, showing q(NOAH_MYJ) - q(NOAH_YSU) for (a) 11Z and (b) 15Z (coloured contours, g/kg). Also shown are the 95% and 100% RH contours for the NOAH_MYJ run, along cross-section AB defined by thered line above.

Conclusions

All runs initialised at 0Z 15th July with GFS analyses

Although this is for a single case, the results suggest that:

The only combination of BL and LSM that produces cloud was NOAH_MYJ. The cloud is reasonably well represented and has realistic initiation and termination times, depth and structure;

The MYJ scheme is preferable to the YSU scheme; the latter is too vigorous in its mixing: moisture is transported away from the BL.

The NOAH land surface scheme provides the necessary surface moisture for the cloud to develop; without it, there is no cloud.

References

[1] http://www.cops2007.de/pics/COPS_TRACKS_english.pdf, http://www.cops2007.de/pics/COPS_TRACKS_deutsch.pdf[2] Wulfmeyer et al. (2008): "The convective and orographically induced precipitation study", Bulletin of the American Meteorological Society, 89, pp1477-1486

A

B